I just did mine at the last appointment I had with my midwife and I was 31 weeks along. I wrote it out according to the book "What to Expect When You Are Expecting", they had a nice list of things to include on the birthplan. And then I took it into my midwife and asked some questions and we adjusted whatever needed to be adjusted. I hear it is best to keep a birthplan to under a page, since they will be referring to it quickly and you don't want to get too wordy. Just put your basic wishes and realize that sometimes they just can not accomodate your wishes (like if the baby is sick or going into distress). But try to talk about it in your early 30-weeks, so you can feel a little more confident going into the labor-impending segment of pregnancy.